Buffering

import { Grid } from 'cx/widgets';

Grid supports buffered rendering which dramatically improves performance with large datasets. Instead of rendering all rows, only visible rows plus a buffer are rendered, enabling smooth scrolling with thousands of records.

 <div controller={PageController}>
  <Grid
    records={m.records}
    keyField="id"
    buffered
    style="height: 400px"
    mod={["fixed-layout", "contain"]}
    cached
    selection={{ type: KeySelection, bind: m.selection }}
    columns={[
      {
        header: "#",
        align: "center",
        children: <div class="cxe-grid-row-number" />,
        defaultWidth: 70,
      },
      {
        header: { text: "Name", style: "width: 100%" },
        field: "fullName",
        sortable: true,
        resizable: true,
      },
      {
        header: "Continent",
        field: "continent",
        sortable: true,
        resizable: true,
        defaultWidth: 130,
      },
      {
        header: "Browser",
        field: "browser",
        sortable: true,
        resizable: true,
        defaultWidth: 100,
      },
      {
        header: "Visits",
        field: "visits",
        sortable: true,
        align: "right",
        resizable: true,
        defaultWidth: 70,
      },
    ]}
  />
</div> 
 class PageController extends Controller {
  onInit() {
    this.store.init(
      m.records,
      Array.from({ length: 5000 }, (_, i) => ({
        id: i + 1,
        fullName: names[i % 5],
        continent: continents[i % 5],
        browser: browsers[i % 5],
        visits: Math.floor(Math.random() * 100) + 1,
      })),
    );
  }
} 
 interface Record {
  id: number;
  fullName: string;
  continent: string;
  browser: string;
  visits: number;
}

interface PageModel {
  records: Record[];
  selection: number;
}

const m = createModel<PageModel>(); 
 import { createModel } from "cx/data";
import { Controller, KeySelection } from "cx/ui";
import { Grid } from "cx/widgets"; 

Name	Continent	Browser	Visits
Alice Johnson	North America	Chrome	97
Bob Smith	Europe	Firefox	8
Carol White	Asia	Safari	11
David Brown	South America	Edge	80
Eva Green	Africa	Opera	100
Alice Johnson	North America	Chrome	60
Bob Smith	Europe	Firefox	72
Carol White	Asia	Safari	18
David Brown	South America	Edge	50
Eva Green	Africa	Opera	34
Alice Johnson	North America	Chrome	78
Bob Smith	Europe	Firefox	77
Carol White	Asia	Safari	44
David Brown	South America	Edge	47
Eva Green	Africa	Opera	20
Alice Johnson	North America	Chrome	95
Bob Smith	Europe	Firefox	40
Carol White	Asia	Safari	30
David Brown	South America	Edge	1
Eva Green	Africa	Opera	53
Alice Johnson	North America	Chrome	23
Bob Smith	Europe	Firefox	62
Carol White	Asia	Safari	28
David Brown	South America	Edge	24
Eva Green	Africa	Opera	66
Alice Johnson	North America	Chrome	20
Bob Smith	Europe	Firefox	29
Carol White	Asia	Safari	96
David Brown	South America	Edge	29
Eva Green	Africa	Opera	63
Alice Johnson	North America	Chrome	48
Bob Smith	Europe	Firefox	49
Carol White	Asia	Safari	98
David Brown	South America	Edge	73
Eva Green	Africa	Opera	46
Alice Johnson	North America	Chrome	13
Bob Smith	Europe	Firefox	27
Carol White	Asia	Safari	56
David Brown	South America	Edge	92
Eva Green	Africa	Opera	62
Alice Johnson	North America	Chrome	34
Bob Smith	Europe	Firefox	56
Carol White	Asia	Safari	96
David Brown	South America	Edge	37
Eva Green	Africa	Opera	87
Alice Johnson	North America	Chrome	14
Bob Smith	Europe	Firefox	69
Carol White	Asia	Safari	63
David Brown	South America	Edge	8
Eva Green	Africa	Opera	25
Alice Johnson	North America	Chrome	3
Bob Smith	Europe	Firefox	50
Carol White	Asia	Safari	83
David Brown	South America	Edge	95
Eva Green	Africa	Opera	32
Alice Johnson	North America	Chrome	88
Bob Smith	Europe	Firefox	73
Carol White	Asia	Safari	96
David Brown	South America	Edge	44
Eva Green	Africa	Opera	36

This grid contains 5,000 rows but renders smoothly thanks to buffered mode. Try scrolling and sorting to see the performance.

How It Works

Enable buffered mode by setting the buffered property. The grid calculates which rows are visible and renders only those plus a configurable buffer for smooth scrolling.

<Grid
  records={m.records}
  buffered
  style="height: 400px"
  mod={["fixed-layout", "contain"]}
  cached
  columns={columns}
/>

For optimal performance, combine buffering with:

Fixed height - The grid needs a fixed height to calculate visible rows
mod="fixed-layout" - Uses CSS table-layout: fixed for faster rendering
mod="contain" - Adds CSS containment for better browser optimization
cached - Prevents row re-renders when unrelated store data changes

Row Numbers

Use the built-in cxe-grid-row-number class to display automatic row numbers:

{
  header: "#",
  defaultWidth: 50,
  children: <div class="cxe-grid-row-number" />
}

Configuration

Property	Type	Description
`buffered`	`boolean`	Enables buffered rendering mode.
`bufferSize`	`number`	Number of rows to render outside the visible area. Default is `60`.
`bufferStep`	`number`	Number of rows to add/remove when scrolling. Default is `15`.
`cached`	`boolean`	Prevents row re-renders when unrelated store data changes. Rows only update when their record data changes.
`lockColumnWidths`	`boolean`	Locks column widths to prevent layout shifts during scrolling.
`lockColumnWidthsRequiredRowCount`	`number`	Minimum number of rows required before column widths are locked.
`measureRowsOnScroll`	`boolean`	Re-measures row heights while scrolling. Useful for variable height rows.